01-04-2016 09:46 AM
1. I want to acquire analog input voltage data with two NI USB 6351 DAQ boards.
2. I'm using chanel no. 0 for both USB 6351 DAQ boards in differential configuration for analog input.
3. I have a single floating voltage signal source ( AC coupled with 70 ohm output impedence ) whose output I'm feeding into chanel no. 0 of both USB 6351 DAQ boards in paralle.
My qustion is: Should I need to provide bias return for analog inputs of both DAQ boards by connecting the negative lead of a floating source to AI GND pin (either directly or through a bias resistor) for both USB 6351 DAQ boards or only for single device? ( Refere to X series user manual for NI 632x/634x/635x/636x/637x Devices, page no.4-11).
01-06-2016 05:30 AM
Hello Jamal,
Based on what you've described I would recommend providing bias return for both devices, but I don't think you will need to do this to obtain the measurements you're looking for. You may want to have a look at this white paper, it's a pretty good summary of all of the grounding considerations you may need to make: http://www.ni.com/white-paper/3344/en/
Best regards,
Jake
01-06-2016 12:39 PM - edited 01-06-2016 12:39 PM
Hello Jake,
I'm using single voltage source as analog input for both DAQ devices, so if I ground negative inputs of both DAQ devices I think it will create ground loop. What do you think in this case?